Torque limiting tools are widely used to tighten a fastener to a specific torque. Such tools are extensively used during surgical procedures, such as an orthopedic surgical procedure. For example, a torque limiting tool may be used to tighten a fastener that is used to secure an orthopedic implant or bone plate. As such, it is often important that the fastener is tightened to a specific torque. Over-tightening a fastener could result in damage to the orthopedic implant or bone plate. Likewise, a fastener that is not adequately tightened may result in undesirable movement of the implant or bone plate within the patient. Such movement of the orthopedic implant or bone plate may be adverse to a patient as the implant may move to a position that does not allow proper bone repair.
In addition, torque limiting tools may also be used to control the amount of torque that is applied during an orthopedic surgical procedure, such as the reaming of a bone. One such procedure is the reaming of the intramedullary canal of a long bone, such as a femur. During the procedure, a cutting tool that is positioned at the end of a shaft is inserted within the intramedullary canal. Torque applied to the shaft rotates the cutting tool so that tissue and bone material are removed from the canal. It is important that an appropriate amount of torque is applied to the shaft during this reaming procedure to ensure that the canal is appropriately reamed. Application of an excessive amount of torque, however, may adversely result in damage to the shaft or the canal. Therefore, it is important that the amount of applied torque is limited to minimize the possibility of causing injury to the patient.
Prior art torque limiters are generally constructed having a complex structure typically comprising a plurality of bias members and ball bearings. During use, the various forces that are applied to these tools generally cause wear of their components which may result in the tool becoming misaligned. As a result, many of the prior art torque limiters require maintenance and calibration. In contrast, the torque limiting device of the present invention comprises two components: a torque drive coupler that mates with a sleeve that is connectable to a drive shaft. Because the torque limiter of the present invention comprises fewer components than prior art devices, the torque limiting device of the present invention is less likely to become misaligned and thus require re-calibration. In addition, the fewer number of components that comprise the torque limiting device of the present invention makes the device more conducive to manufacture.
More specifically, the tool and the torque limiting mechanism of the present invention comprises a sleeve having a plurality of longitudinally extending first lobes that outwardly project from the annular sidewall of the sleeve. A first groove is positioned longitudinally between two adjacent first lobes. A drive shaft is positionable within at least a portion of a throughbore that extends through the sleeve. The drive coupler comprises a socket defined by an annular coupler sidewall within which the sleeve is received. A plurality of longitudinally extending second lobes outwardly project from an interior surface of the annular sidewall within the coupler socket. In addition, a second groove is positioned longitudinally between two adjacent second lobes.
The sleeve and the coupler socket are configured so that they mate together. The plurality of first and second elongated lobes of the sleeve and coupler socket are received within a corresponding first and second grooves of the sleeve and coupler socket. Rotation of the coupler causes a physical interference of the mated lobes of the sleeve and coupler socket that results in torque being transferred from the coupler to the sleeve and connected drive shaft. When the magnitude of torque applied to the coupler exceeds a torque limit, the coupler and sleeve become disengaged. The respective first and second lobes of the sleeve and coupler socket ride out of their corresponding second and first grooves when a torque limit is exceeded.